This proposal is concerned with identifying the components of the egg that are formed during oogenesis that specify the pattern of cleavage which occurs during the first stages of embryogenesis and which represent the localizations of developmental potential which bias the way in which different regions of the egg will differentiate during embryogenesis. One system that will be investigated is the ctenophore egg. I have worked out a description of how the localizations of developmental potential that specify comb plate cilia cells and photocytes are set up prior to the differential division which restricts these factors to separate blastomere lineages during the first stages of development. This proposal will try to identify the parts of the cell where these factors reside before and after they become localized. The other problem that will be studied in this proposal concerns the developmental basis for dextral and sinistral symmetry in gastropod molluscs. I have demonstrated that eggs from dextral snails contain a cytoplasmic substance which causes sinistral eggs to show the cleavage pattern of dextral snails and to develop into dextral snails when this substance is injected into sinistral eggs prior to second polar body formation. This part of the proposal will try to establish how this substance changes the cleavage pattern of the sinistral egg.